A vinyl alicyclic hydrocarbon polymer is prepared by hydrogenating an aromatic ring of a vinyl aromatic polymer, for example, polystyrene. The vinyl alicyclic hydrocarbon polymer is excellent in heat resistance, transparency, low water absorption property, etc. and is hence proposed to be used as a forming or molding material for optical disk substrates. The vinyl alicyclic hydrocarbon polymer is also excellent in chemical resistance, low dissolution property, etc. and is hence proposed to be used as a forming or molding material for medical containers (Japanese Patent Application Laid-Open No. 6-199950).
As described above, the uses of the vinyl alicyclic hydrocarbon polymer are about to be spread. In order to more develop the uses thereof, however, it is necessary to improve it in such a manner that various high properties required of each use can be exhibited while retaining its characteristic excellent properties such as high heat resistance and transparency, and low water absorption property.
Examples of new uses of the vinyl alicyclic hydrocarbon polymer include a light guide plate for a plane emission illuminator used in a back light or front light in a liquid crystal display device (LCD). In recent years, LCDs have been spread as display devices in computers or car navigation systems. The display by LCD is inconvenience in use at a dark place because the LCD itself is non-luminous. Thus, a plane emission illuminator uniformly illuminating a display part of the LCD has been developed for the purpose of permitting improvement in ease of seeing and use at the dark place. In a light transmission type LCD, a back light type that illumination is performed from a back side of a display surface is used, while a front light type that illumination is performed from a front side of a display surface is used in a light reflection type LCD.
Plane emission illuminators are roughly divided into an edge system and a vertical system according to the arrangement of a light source to the display surface. In the back light type, either the edge system or the vertical system is selected as necessary for the end application intended. In the case of the front type, the edge system is used.
FIG. 1 illustrates a cross-sectional view of an exemplary back light of the edge system. A reflection layer 2 for diffusely reflecting light is provided on a back surface of a transparent light guide plate 1. The light from a light source 4 (for example, cold cathode-ray tube) arranged at a side surface of the light guide plate 1 is diffusely reflected or scattered by the reflection layer 2 and collected on the side (upper side in the drawing) of a liquid crystal display panel. A diffusion plate 3 is arranged on the surface of the light guide plate 1 on the side of the liquid crystal display panel as needed. Further, a condenser plate (not illustrated) may be arranged thereon. A reflection plate may be arranged under the reflection layer 2 as needed.
The light guide plate is formed from a transparent synthetic resin such as an acrylic resin for weight saving. As the reflection layer, an ink pattern may be formed on the reflection surface of the light guide plate by printing. Besides, there are reflection layers of various types, such as those obtained by matting the reflection surface of the light guide plate, converting it into a Fresnel mirror or vapor-depositing aluminum thereon. The plane emission illuminator of the edge system may be made thin in thickness or large in size.
The light guide plate for the plane emission illuminator is required to have a high available efficiency of light from a light source (lamp), thereby permitting high luminance, deteriorate physical properties thereof by heat generated from the lamp and have excellent light-resistance stability.
As described above, the vinyl alicyclic hydrocarbon polymer is excellent in heat resistance, transparency, low water absorption property, etc. and hence attracts attention as a forming or molding material for light guide plates for the plane emission illuminators. However, a light guide plate formed with the vinyl alicyclic hydrocarbon polymer involves problems that it is colored by long-term use, and gases of a volatile component or the like are generated to cloud a cold cathode-ray tube (lamp) or a lamp reflector covering the cold cathode-ray tube. Therefore, the vinyl alicyclic hydrocarbon polymer does not fully satisfy high properties required of the use as the forming or molding material for the light guide plates for the plane emission illuminators.